1. Field of the Invention
The present invention relates to a base of a housing of a driver side gas generator or inflator for a vehicle safety system, and more particularly, to a base of which a majority of the features are stamped from a thin sheet of material.
2. Description of the Related Art
Gas generators or inflators which use combustible solid fuel gas generant compositions for the inflation of inflatable crash protection or air bag restraint systems are known in the prior art.
One type of inflator, such as a driver side inflator apparatus, comprises a housing made of an upper shell or diffuser and a bottom shell or base. A plurality of concentric cylinders are formed in the diffuser. The cylinders together with the base form various chambers in the housing, an outer diffuser chamber, an inner ignitor chamber and a middle combustion chamber.
In operation, a crash sensor sends an electrical signal to an initiator or squib. The squib fires into the ignitor chamber and ruptures a container, which holds an ignitor material, commonly a mixture of boron and potassium nitrate. The ignitor material burns with a very hot flame and ignites solid fuel gas generant pellets contained in the combustion chamber. The pellets release a nitrogen gas, which travels through the diffuser chamber and into a protective air bag for protecting occupants of the vehicle.
Due to the enormous mechanical and thermal stresses produced, gas generators must be made from strong materials. U.S. Pat. No. 4,547,342, assigned to the assignee of the present invention, the disclosure of which is herein incorporated by reference, discloses a two-piece light weight aluminum inflator housing strong enough to withstand the associated stresses. Specifically, the inflator includes an aluminum diffuser shell and base shell, which are impact forged, heat treated and then finally machined to produce an inflator having the desired strength and shape.
Using an impact forging process for forming a part is well known in the art. During the impact forging process, the material to be processed, e.g. the slug, is placed into a die. The stroke of the die press causes the punch to force the material through openings between the punch and the die, or into cavities in the punch or die.
A disadvantage with the prior art impact forging process, is that a forged housing base requires excessive machining to form the base in its desired final shape. FIG. 1 illustrates a base 10' which has been formed by the impact forging process. The as forged part is shown by dashed line and the final shape of the part is indicated by the solid line. As shown, numerous areas of the forged base must be machined after the formation of the part. This significantly increases manufacturing cost and time.
U.S. Pat. No. 4,530,516, assigned to the assignee of the present invention and herein incorporated by reference, discloses an inflator housing including a housing structure comprising a stamped diffuser and base. Both the base and diffuser are significantly simpler in design than the other prior art inflator housing components. The base does not include weld lands, a squib pocket or an attachment flange. Also, the diffuser does not include concentric cylinders forming separate chambers. Due to the simplicity of the diffuser and base, extra parts, such as a cap, which holds the base and diffuser together, are required. This also significantly increases manufacturing time and cost.
Another disadvantage with the prior art stamped base is that the diffuser and base are electron-beam welded together, which is complex and time consuming. Electron beam welding is a well known process which involves fusion by local melting produced by bombardment of a high velocity stream of electrons.
Therefore, in order to continue to decrease manufacturing time and cost, it is desirable to produce a driver side inflator base, which can be manufactured simply and quickly.